1
Distribution of Earth’s water
Fig. 10.2, p. 267
2
The hydrologic cycle
Processes involved in the hydrologic cycle:
Fig. 10.3, p. 267
Evaporation & Transpiration
Precipitation
Infiltration & Runoff
3
The Hydrologic Cycle
4
Drainage basin
Def.: The entire area from which a stream and its tributaries receive their
water
Separated from another drainage basin by a divide
http://www.ndsu.nodak.edu/tricollege/watershed/image/wpe1.gif
5
Drainage Basins and Divides
Def. Divide: a line that separates two drainage basins
Fig. 10.30, p. 289
6
Mississippi River drainage basin
7
Rivers of North America
(lots of them flow Northward!)
8
Picture: The "Continental Divide," the line that separates the Nelson/Red River drainage basin from the Mississippi/James
drainage basin is marked by a sign along I_94, midway between Valley City and Jamestown, ND.
9
Classification of Streams
Fig. 10.31, p. 290
http://www.worldatlas.com/webimage/countrys/namerica/printpage/nanewriv.htm
Drainage Patterns
Flow
10
Drainage Patterns
Def: Pattern of the interconnected network of streams in an area
3 common:
Dendritic
Radial
Rectangular
(Trellis)
11
Drainage Patterns
Fig. 10.32, p. 291
12
Dendritic drainage pattern
13
Flow
Does the stream flow on a regular basis or not?
3 types:
Perennial
Intermittent
1
Ephemeral
14
Stream flow
Velocity
Gradient
Discharge
15
Velocity
ft/sec
or
metric equivalent
Fig. 10.5, p. 269
16
Gradient
The slope, or vertical drop per distance
ft/mile or metric equivalent
Fig. 10.7, p. 271
17
Discharge
Def: the volume of water moving past a given point per unit time
CFS = cubic feet/second = ft3/second = channel width x channel
depth x velocity
Ex: 100ft (width) x 15ft (depth) x 6 ft/sec = 9000 ft3/sec
18
Laminar vs. Turbulent Flow
Laminar: Water flow parallel to bed of stream
Turbulent: Disrupted flow
19
Velocity
ft/sec
or
metric equivalent
Fig. 10.5, p. 269
20
“Ideal” vs. Typical stream channel velocity profile
21
22
Factors that change downstream:
INCREASE:
Velocity (because of greater discharge, smoother and larger channel)
Discharge
Channel size (larger, smoother channel, greater discharge)
DECREASE:
Gradient
Channel roughness
23
Transported material: the stream load
Load: The quantity of material transported by the stream
2
Capacity: the maximum load a stream can transport
Competence: the maximum SIZE particle a stream can transport
24
1) Dissolved load
Mostly from groundwater leaching of soils and bedrock
Amount not dependent on stream energy
Quantity depends on climate
25
26
2) Suspended load
Largest part of the load
Controlled by water velocity and the settling velocity of each particle
Usually silt or clay
27
28
Diagram of Load types
29
3) Bed load
Suspended load
Coarse particles that move along the stream bottom
Rolling
Sliding
Saltation (jump, skip, leap)
Do not move constantly
<10% of a stream’s load
30
31
Classification of Particle Size
Gravel
Pebble-cobble-boulder
> 2.0 mm
Sand
0.06 - 2.0 mm
Silt (gritty in your teeth)
0.004 - 0.06 mm
Clay (smooth in your teeth)
< 0.004 mm
32
Erosion, Transport and Deposition
Hjulström Diagram
Velocity vs. Particle Size
33
Hjulström Diagram
OBSERVED
erosive
power
3
34
Is there a downward limit to stream erosion?
Yes, the downward limit is the base level, the lowest point to which a
stream can erode
Two general types of base level:
Ultimate (sea level)
Local (temporary)
35
Longitudinal profile of a stream
36
Changing stream conditions cause:
Readjustment of stream activities
Raising base level causes deposition
Lowering base level causes erosion
37
A waterfall is an example of a local base level
38
Can streams achieve equilibrium?
A graded stream is in equilibrium
neither eroding nor depositing material but:
only transporting material
a self-regulating system, constantly adjusting toward equilibrium
39
40
41
Fig. 10.8, p. 273
Longitudinal profile of a stream
Graded stream
4